Cookware coated with fluoropolymers, especially polytetrafluoroethylene (PTFE), has come into widespread use in recent years. Many cooks prefer to use such cookware because of its non-stick properties and because it is so easy to clean.
It is well known that the adhesion of fluoropolymers to metal is of a rather low order, so in the fabrication of such cookware it is customary to improve adhesion by applying a primer composition to the metal before applying the fluoropolymer topcoat. Such a primer composition is described in U.S. application Ser. No. 588,005, filed June 18, 1975. The composition described there comprises
A. a fluoropolymer, PA1 B. a binder comprising colloidal silica and the amine salt of a polyamide acid, PA1 C. a coalescing agent, PA1 D. a liquid carrier. PA1 .fwdarw. denotes isomerism; PA1 R is a tetravalent organic radical containing at least two carbon atoms, no more than two carbonyl groups of each polyamide acid unit being attached to any one carbon atom of said tetravalent radical; PA1 R.sub.1 is a divalent radical containing at least two carbon atoms, the amide groups of adjacent polyamide acid units each being attached to separate atoms of said divalent radical; PA1 n is a number large enough to give the polyamide acid an inherent viscosity of at least 0.1, measured as a 0.5% solution in N, N-dimethylacetamide at 30.degree. C. PA1 N-methylpyrrolidone PA1 dimethylformamide PA1 dimethylacetamide PA1 dimethylsulfoxide PA1 cresylic acid PA1 sulfolane PA1 formamide.
And
While cookware primed with such a composition is quite durable, its entire fluoropolymer coating tends to become scratched after extended use.